In LTE (Long Term Evolution), specifications of which have been designed in 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, a user terminal executes a random access procedure for establishing a connection with a cell.
Further, in the 3GPP Release 10 and thereafter, a carrier aggregation is supported where a user terminal simultaneously uses a plurality of component carriers (plurality of cells) to perform communication. In the carrier aggregation, a cell that performs mobility control of a user terminal is called a primary cell (Pcell), and an auxiliary cell with which to form a pair with the Pcell is called a secondary cell (SCell).